Siberian Federal University

Issue

Journal of Siberian Federal University. Engineering & Technologies. 2010 3 (1)

Authors

Hagstrum, Jonathan T.; Firestone, Richard B.; West, Allen; Stefanka, Zsolt; Revay, Zsolt

Contact information

Hagstrum, Jonathan T. : U.S. Geological Survey, 345 Middlefield Road, Menlo Park; CA 94025, United States, e-mail: ; Firestone, Richard B. : Lawrence Berkeley National Laboratory, Berkeley; CA 94720, United States,; West, Allen : GeoScience Consulting; Box 1636, Dewey, AZ, 86327, United States,; Stefanka, Zsolt : Institute of Isotopes of the Hungarian Academy of Sciences; H - 1525 Budapest, P.O.B. 77, Hungary,; Revay, Zsolt : Institute of Isotopes of the Hungarian Academy of Sciences; H - 1525 Budapest, P.O.B. 77, Hungary,

Keywords

global climate changes; megafauna; micrometeorites; multiple impacts; Siberian bison skull; Pleistocene Alaskan mammoth tusks; plasma mass spectrometry analyses; X-ray fluorescence analyses; electron microprobe analyses; gamma-ray activation analysis; scanning electron microscope images

Abstract

We have discovered what appear to be micrometeorites imbedded in seven late Pleistocene Alaskan mammoth tusks and a Siberian bison skull. The micrometeorites apparently shattered on impact leaving 2 to 5 mm hemispherical debris patterns surrounded by carbonized rings. Multiple impacts are observed on only one side of the tusks and skull consistent with the micrometeorites having come from a single direction. The impact sites are strongly magnetic indicating significant iron content. We analyzed several imbedded micrometeorite fragments from both tusks and skull with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and X-ray fluorescence (XRF). These analyses confirm the high iron content and indicate compositions highly enriched in nickel and depleted in titanium, unlike any natural terrestrial sources. In addition, electron microprobe (EMP) analyses of a Fe-Ni sulfide grain (tusk 2) show it contains between 3 and 20 weight percent Ni. Prompt gamma-ray activation analysis (PGAA) of a particle extracted from the bison skull indicates ~0.4 mg of iron, in agreement with a micrometeorite ~1 mm in diameter. In addition, scanning electron microscope (SEM) images and XRF analyses of the skull show possible entry channels containing Fe-rich material. The majority of tusks (5/7) have a calibrated weighted mean ¹⁴C age of 32.9 ± 1.8 ka BP, which coincides with the onset of significant declines <36 ka ago in Beringian bison, horse, brown bear, and mammoth populations, as well as in mammoth genetic diversity. It appears likely that the impacts and population declines are related events, although their precise nature remains to be determined.

Pages

123-132

Paper at repository of SibFU

https://elib.sfu-kras.ru/handle/2311/1635

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).